Recent evidence suggests that a complex neural circuitry, the components of which may communicate with each other by diverse neurochemical signals, participates in initiation and sustenance of preovulatory LHRH and LH hypersecretion. This proposal focuses on contributions of the peptidergic components of this neural circuitry. The precise modes of involvement of an excitatory component - neuropeptide Y (NPY), and an inhibitory component - endogenous opioid peptides (EOP) in the preovulatory LH discharge will be studied. NPY participation will be examined by studying the dynamic changes in hypothalamic NPY levels and release rates preceding and following the LH surge. Whether NPY acts independently or in concert with excitatory adrenergic transmitters or whether adrenergic transmitters mediate NPY excitation of LHRH and LH release will be the subject of intensive investigations. Curtailment of the inhibitory influence of EOP as an early neurochemical event responsible for triggering the excitatory neural chain on proestrus, will be documented by analysis of beta-endorphin (betaE) release in association with the LH surge. Experiments are designed to test whether EOP exert a "braking" influence on basal episodic LH secretion during the estrous cycle and to ascertain the roles played by NPY and adrenergic transmitters in mediating EOP effects on LH release. The release of NPY, betaE, LHRH and neurotransmitters will be assessed in vivo by push-pull cannulate and in vitro by hypothalamic perifusion methods. In vivo experiments will utilize chronic intraventricular cannulae for continuous or episodic delivery of test materials and blood sampling by intrajugular cannulae in freely-moving rats. In some experiments, neuropeptides will be measured in microdissected brain sites. Neuropeptides and LH will be measured by RIA and catecholamines by radioenzymatic assays and HPLC.